DESCRIPTION: Ozone produced in photochemical smog poses a significant health risk in the Los Angeles Basin. A complete understanding of the chemistry involved in ozone formation is required in order to formulate proper regulations of chemical emissions that are most effective in reducing the smog problem. Peroxy radicals are precursors in the formation of tropospheric ozone via reaction with NO and NO(2). Rate coefficients for these reactions for hydrocarbons larger than ethane have not been measured. In this study, rate coefficients for the reaction of alkyl peroxy radicals deriving from C(3)-C(8) alkanes with NO, NO(2), and their self-reaction will be measured using a technique of pulsed infrared laser thermal lens spectrometry to monitor the peroxy radical concentration as a function of time. The mechanism for peroxy radical formation and subsequent reactions is RH + Cl --> R + HCl hydrogen abstraction R + O(2) + M --> ROO + M peroxy radical formation ROO + NO --> RO + NO(2) nitrogen dioxide formation ROO + NO2 + M --> ROONO(2) + M peroxy acyl nitrate formation ROONO(2) + M --> ROO + NO(2) + M peroxy acyl nitrate decomposition ROO + ROO --> ROOR + O(2) peroxide formation where Cl is produced from the flash photolysis of Cl(2) by a xenon flashlamp. The gas mixture composition is adjusted in order to isolate specific ROO product channel reactions. A vibrational mode of ROO is excited with a pulsed CO(2) laser, and the thermal gradient resulting from the release of energy to translation degrees-of-freedom is probed with a cw HeNe laser. The change in intensity of the HeNe laser as the thermal gradient forms is monitored by a photodiode. The magnitude of the thermal lens signal is proportional to the ROO concentration. By varying the time delay between the flashlamp and the CO(2) laser pulses, the kinetic information for removal of ROO will be determined. Rate parameters will be obtained by fitting the raw data to a complete reaction mechanism using least-squares techniques. From this analysis scheme, rate coefficients will be determined for reactions of peroxy radical with NO and NO(2) as well as the ROO self-reaction.